The present invention relates to memories and more particularly to hierarchical memories.
Hierarchical memories using monolithic storage elements at the higher levels have resulted in faster and more economical memory systems as described in the Brickman et al U.S. Pat. No. 3,806,888. However, such memories are not without drawbacks. In particular, hierarchical systems have significant communication problems between the levels of the hierarchy and the volatile monolithic memories in the higher levels of the hierarchy have data integrity problems resulting from their reliability and their susceptibility to power supply failures and fluctuations. One solution to the integrity problem would be to have two storage units at each level, each with a duplicate of the data at the level so that if a failure occurred in one store, the data could be reproduced from the other. However, while this improves reliability it does nothing to alleviate the communication problem between the levels and, furthermore, in case of a failure requiring or forcing a shut down of the memory the transfer of the duplicated data from the levels of the memory containing the volatile memories to levels containing non-volatile memories in the process of bringing the storage system down would require much more time than is desirable and in fact may be available before the failure results in the destruction of data.